Means for controlling electrical transmission



I Feb: y J. S. JAMMER MEANS FOR CONTROLLING ELECTRICAL TRANSMISSIONFiled June 17 2 flwew/orf Jaco J. Jam 6/ y moon s. June, or new our, a.v., assrenon r wrsrnan nancrnrc com,

mcoaroaarnn, or new YORK, n. r, a conrorron or new YORK.

MEANS FOR CONTROLLING ELECTRICAL TRANSMISSION.

Application filed June 17, 1922. Serial 1E0. 568,9l0.

I. To all whom it may concern: potentiometer setting cannot entirelycom- 1t known that l, JACOB S. JAMMER, a pensate for these changes,inasmuch as citizen of the Umted States, residing at New changes in thesetting of the usual type of York, in thecounty of New York, State ofsimple potentiometer cause repeater gain cycles.

New York, have invented certain new .and .changes which are equal at allfrequencies. useful Improvements in Means for Control- The most completecompensation can only 1111 Electrical Transmission, ofwhich the beobtained by means for producing transfollowing is a full, clear,concise, and exact mission'gains or losses varying with ire--description. quency.

The invention relates to means for 6011- The present invention providesan attenutrollin'g'the transmission gain or loss in a ating deviceadjustable to give changes in line transmitting currents of differentfreits transmission gain or loss which vary with quencies, for instancea telephone line transfrequency, and further, to provide such adeinitting different frequencies in the voice vice wherein movement of asingle element frequency range, or a carrier line transinay cause theadjustment necessary to efiect mitting frequencies, for example, as highas ;=the var ing changesof gain or loss. 30,000 cycles per second and aslow as 6,000 Anot e1- object is to provide a repeater comprising such adevice, the device embody-- It is customary, in long lines of suchchar-' ing resistance, inductance and capacity. so acter, to insertrepeaters giving transmisproportioned and arranged that adjustment siongains tending to counteract the attenuy-of the -device may be made to sochange ating effect of the line upon the currents the gainof therepeater by. different-amounts transmitted. Ordinarily a potentiometeris for difiierent frequencies as to compensate associated with therepeater, in order thatzfor changes in attenuation, due to weather whenthe line attenuation increases or dechanges forfinstance, in the line inwhic creases the potentiometer setting may be 'corthe repea er is6011116095861 respondingly adjusted to cause the repeater Ahother objectis to provide an attenuat gain to be increased or decreased by an ingdevice of the type referredtodn the amount approximately the lineattenuation form of a v ge changing potent ometer change as nearly aspossible. However, the possessing inherent transmission equalizing usualchanges of line attenuation are greater properties. v co for thecurrents of the higher frequencies In the embodiment disclosed,thepotentibeing transmitted over the line than for the ometer devicecomprises a resistance and an currents of the lower frequencies passinganti-resonant loop for serial connection beover the line. This is trueboth as regards tween the inputleadsto the device, and means cases wherecurrents'of the voice frequency for varying the amount of the seriesresist-- range are being transmitted and as regards ance in circuit and,1n efiect, simultaneously cases where currents of higher frequencies,adjusting the output leads from the device to for instance 6,000 cyclesand 30,000 cycles connect them across the loop and the proper are beingtransmitted. In the former cases. proportion of the series resistance incirthe predominating influence in causing cuit to cause the device todiscriminate to the aochange of line attenuation usually is changedesired degree against the transmission of in the temperature of theline and in the relatively high frequenmesfrom the input latter casesthe predominating influence genleads to the output leads in favor of theerally is change of specific inductive catransmission of relativelylower frequencies pacity of the medium surrounding the from the inputside to the output side of line, due to change of dampness. Since thethe device. As is explalned herelnafter, the changesct line attenuationvary with frepurpose of this frequency d1SOI1m1 Ila.tl0n is quency, itis clear that merely shifting the to cause a-disthrtion of the transmtted currents complementary to that due to the unequal line attenuationof the different frequencies, in order to neutralizethe d1stor tion dueto such inequality of line attenuation.

. I Fig. 1 shows a repeater circuit embodyeter consisting of resistances11 and 12 and adjustable .contacts13 and 14 which may be so connectedmechanically by suitable means (not shown) as to move toward or fromeach other simultaneously. A transmission equalizing shunt is provided,

consisting of inductance 20, capacity 21,

resistances 22 and 23, and adjustable contacts 24 and 25, electricallyand mechanically connected to contacts 13 and 14, respectively. Theinductance and capacity are tuned to a frequency lower than, orsubstantially equal to, the lowest frequency to be repeated; In atypical case where frequencies covering a range of from 6,000 to30,000Qcyles are to be repeated, the inductance has a value ofapproximately 150 mil henries, the capacity is of such value as toresonate with the inductance at about 6,000 cycles, the resistances 22and 23each have a; maximum value of about 15,000 ohms, and theresistance 11- and 12 each have a maximum value of about 48,000 ohms.

When the contacts 24 and 25 are set to cut all or nearly all of theresistance 22, 23 out of circuit, the impedance of the part of theequalizing shunt that is included between the contacts 24 and'25 is ofcourse, very low for the frequency of 6,000 cycles to which-theinductance and the capacity are tuned, and increases With frequency sothat the impedance of this part of the shunt is materially higher for30,000 cycles than for 6,000 cycles. In other words, a curve plottedbet-ween impedance of this part of the shunt as ordinates and frequencyas abscissae, sloped downward, or gradually falls, from the 30,000cycles point to the 6,000, cycle point; If the setting of contact-s 24and 25 be changed to include all or a large portlhn of the resistances22 and 23 in circuit, the impedance frequency curve for the part of ,theequalizing shunt that is then included in the circuit will fall moregradually from the 30,000 cycle po1nt to the 6,000 cycle point, for theim- 1 pedance at 6,000 cycles will be increased this frequency is highcompared to the inpedance of the resistance 22 and 23 and is practicallyat right angles to the resistance component of the impedance. Thus, asthe contacts 24 and 25 are moved toward each other, the effect of theequalizing shunt is to tend to reduce the repeater gain more for thelower frequencies of the frequency range between 6,000 and 30,000 cy;cles than for the higher frequencies of this range. Therefore, when lineattenuation decreases and the contacts l3 and 14 of the potentiometer'10 are moved toward each other to reduce the repeater gain sufhcientlyto approximately counteract the decrease of line attenuation for30,000cycles, that is, sufiiciently to maintain the difference betweenthe transmission level at the transmitting end and that at the receivingend of the line section the transmission loss of which the repeater isintended to control, approximately constant for 30,000 cycle current,the simultaneous movement of the contacts' 24 and 25 toward each othercauses the equalizing shunt to tend to increase the repeater gain for6,000 cycle current without tending to materially increase it for 30,000cycle current; and the difference between the amount of repeater gainthat a given change in adjustment of the/ shunt by the change of settingof contacts 24 and 25 tends to effect for low frequencies and thevamount that it tends to effect for high frequencies should, of course,be made approximately equal to the arithemetical dif ference between thedecrease ofline attenuation for the high frequencies and thedecreases ofline attenuation for the low frequencies. A battery 26 maintains grids27 and 28 of the second stage of the repeater at potentials such thatthese grids draw substantially no current. It is, of course; to beunderstood that the expression low frequencies here refers to quenciesof the frequency range transmitted, and not to the frequencies below thereso- "nance frequency of the equalizing shunt. It

course, that in stating that the changes of distortion prois also to beunderstood, of

duced by the potentiometer and equalizing shunt should be equal andopposite to those due to the line attenuation, the line referred to isthe section of line the transmission loss of which the repeater isintended to control. a two stage, push-pull electron discharge repeateris shown for repeating from a line section 3, which extends West to aline section 5 which extends east. The first stage of the repeater feedsthe second stage .through a gain adjusting pothe lower fre- 31, 32, and33, a resistor composed of sections 34, 35, and 36, tap connections 3738,

:39, 40, 41 42, 43, and 44 leading from the ends of. the resistorsections, contacts 45 and 46"adjustable for connection to the free endsof the tap connections, and a loop circuit comprising capacity 47 andinductance 48 connected between the resistor sections 33 and 34. Theloop circuit is tuned to a frequency higher than, or approximately equalto, the highest frequency that is to be repeated. The tap connectioncomprises little or no resistance. The tap connections 37, 38, and 39are resistance tap connections, the resistance comprised in tapconnection 39 being great in comparison to the resistance of theresistor section 33, the resistance of tap connection 38 bei larger thanthat of ta connection 39 an being great 7 in comparison to that ofresistor sections 32 and 33 in series, and the resistance of tapconnection 37 being larger than that of tap connection 38 and beinggreat in com-' parison to that of resistor sections 31, 32, and 33 inseries. The part of the potentiometer shown below the tuned loop circuitis symmetrical with the part above the loop, and contacts 45 and 46 arepreferably connected mechanically by means (not shown) whei'eby thesecontacts may be moved simultaneously toward or away from each other. Abattery 26 maintains the grids 27 and 28 of the second stage of therepeater at potentials' such that these grids draw substantially nocurrent.

As the contact 45 is movedfrom a tap connection of one resistance valueto the next tap connection of higher resistance the amount of resistancein series circuit be-' tween the contact 45 and the tuned loop increasesby the sum of the resistance of the resistor section between the two tapconnections plus the difference between the resistances of the two tapconnections; and the potential of the grid 27" is aifected as thoughvthe connection of the grid were simultaneously shiftedfrom theright-hand end of the tap connection of lower resistance 'to theright-hand end of the other, or higher resistance tap connection. Theoperation of the part of the potentiometer that is shown .below thetuned loop will, of course, be the same as the operation of the partshown above the loop.

Supposing that frequencies covering a.

range from 6,000 cycles to 30,000 cycles, for example, are to berepeated, and that the capacity 47 and inductance 48 are tuned to 30,000cycles, then when the cbntacts 45 and 46 are set on low resistance tapconnections 40 and 44, the voltage drop across the tuned across thegrids 27 and 28 (half of which latter voltage is applied to the circuitof one of the grids, the other half being applied to the other grid),is, of course, relatively high for the resonant frequency of 30,000cycles, and decreases with frequency to a comparatively low valuefor afrequency of 6,000 cycles. In other words, a curve plotted betweenimpedances across the loop as ordinates and frequencies as abscis- -saeslopes downward, or gradually falls from the 30,000 cycle point to the6,000 cycle point. Whenline'attenuation decreases, contacts 45 and 46are moved'away from each other to increase the ratio of the impedance ofthe part of the potentiometer in circuit therebetween to the impedanceof the part of the potentiometer, the-voltage drop across which is thealternating voltage across grids 27 and 28. The effect df increasing theamount of the resistance of tap connections 37 to 44 that is included incircuit, is to tend'to reduce the repeater ain sufficiently to more thancounteract the ecrease of line attenuation at all frequencies. However,the simultaneous effective shifting, of the connections of the grids 27and 28 to the potentiometer to include between the effective points ofconnection an increment of impedance that is relatively greater at 6,000cycles than at 30,000 .cycles, tends to increase the repeater gain for6,000 cycle current more than .for 30,000 cycle current. The difference.between the gain decrease that the changeof setting of thepotentiometer produces for high frequencies and the gain decrease thatit produces for currents of low frequencies in the frequency range to betransmitted, should be made approximately equal to the differencebetween .the decrease of lineattenuation for the high frequencies andthat for the low frequencies.

Y Preferably, i determining the proper values forthe resistances ofsection 31 to 36 and tap connections 37 to 44, these resistances arefirst calculated approximately, in the manner indicated below, andtheactual values to be used are then ascertained by trial. i

Fig. 3 is designed to facilitate explanation of the method ofcalculating the resistance values approximately. In this figure Erepresents the volta generated in the tubes of the first ampli er stageof Fig. 2, Z represents the plate filament impedance. of the tubes ofthe first stage, Z represents the impedance presented across grids 27and 28 and is assumed to be large in comparison with impedances Z Z Z ZZ repre sents the impedance of the part of resistance sections 31 to 36which lies between the two tap connections to which the potentiometerinput leads are connected at any given time, Z representsthe impedanceof the tap connection on which the input leads terminate at that time, Zrepresents the impedance of the tuned lop 47-48, and E represents thevoltage across grids 27 and 28.

The current flowing through the input leads into the potentiometer is ML"Z,+Z,+Z,+Z, and E will equal I (Z +Z which equals The attenuationproduced by the potentiometer equalizer is f and this ratio may beconverted to loss in 800 cycles miles of standard 19 gauge cable bymultiplying the log of the reciprocal of the ratio by 21.13, inaccordance with the commonl used formula, miles loss=21.13 0/ e) Let itbeassumed that the known value of Z 4 is 12,000 ohms, and that the totalgain produced in the amplifying elements of the repeater is miles,(regardless of frequency), and that the line loss under the mostunfavorable weather conditions can be taken t0 be 18 miles more for 30kilocycle current than for 6 kilo-cycle current. Then it will benecessary for the potentiometerequalizer (when at its highest gainsetting) to produce for the 6 kilo-cycle current a loss 18 miles greaterthan the loss produced for 30 kilo-cycle current; or in other words, thepotentiometer-equalizer loss for 6 kilocycle current must be somewhatinexcess 30 kilo-cyc preciable.

of 18 miles since even its minimum loss for,

le current will, of course, be ap The impedance Z should be made highenough for 30 kilo-cycle current, to prevent this minimum loss from beinexcessive, but must be made low enough or 6 kilo-cycle current to havethe potentiometerequalizer'loss for the 6-kilo-cycle current in excessof 13 miles when the potentiometerequalizer is at its lowest gainsetting Assame a value of say 50,000 ohms for Z at 30 kilo-cycles. Thenfor this frequency the potentiometer-equalizer loss with thepotentiometer-equalizer at its highest gain setting will be p o Then,since the potentiometer-e ualizer at 21.13 log =2 miles. v I (I itshighest gain setting is to pro uce a loss for 6 kilo-cycle current 18miles greater than its loss for 30 kilo-cycle current, its loss for 6kilo-cycle current must be 18-1-2 miles, or

20 miles, at this setting. Having determined this loss, the value of Zfor 6 k110- cycle current can be obtained as follows:

whence Z +l500 ohms.

e may now proceed to calculate the values that Z and Z should have forsome other setting of the potentiometer, say for the lowest gainsetting-that is, the setting in which contacts 45 and 46 are on tapconnections 40 and 44, respectively. Let it be assumed that the maximumgain change to be produced for 30 kilo-cycle current by changing thesetting of the potentiometerequalizer is 13.5 miles, or, in other words,that the minimum gain of the repeater for 30 kilo-cycle current is to be(30 -2) 13.5:

2813.5:14.5 miles, or, inunther words, that the maximum loss to beproduced by the potentiometer-equalizer for 30 kilo-cycle current is tobe 15.5 miles, or, in other words, that for the lowest repeater gainsetting of the potention1eter-equalizer the loss produced by that devicefor 30 kilo-cycle current is to be 15.5 miles=21.13 log Z,+50,000 1Z,+Z,+50,000+12,000

and let it be further assumed that the line characteristics are suchthat the maximum gain change to be produced for 6 kilo-cycle current bychanging the setting of the potentiometer-equalizer is 5 miles, or, inother words, that the minmum gain of the repeater for 6 kilo-cyclecurrent is to be (3020)5 :105:5 miles, or, in other words, that themaximum loss to be produced b the potentiometer-equalizer for 6kilo-cycfe current is to be 25 miles, or, in other Words, that for thelowest repeater gain setting-of the potentiometer-equalizer the lossproduced by that device is 25 miles =21.13 log% =21.13 log We may nowsubstitute numerical trial a contacts 45 and 46 on tap connections l0and 41, respectively will be 10 miles for 6 kilocycle current and 28miles for 30 kilo-cycle current; and when the contacts 45 and 46 aremoved to tap connections 37 and *1 the gain will be ieduced to 5 milesfor 6 kilocycle current and to 14.5 miles for 30 kilocycle current.Thus, the change of setting will reduce the gain for 30 kilo-cyclecurrent by 13.5 miles and will reduce the gain for 6 kilo-cycle currentby only 5 miles.

The proper values of resistances 38, 39, i2, -13, 31, 3:2, 33, 3- 35,and 36, in Fig. 2, necessary to give the repeater gains requisite tocompensate for changes of line attenuation varying with frequency may bedeterlnined in the fashion in which the impedances Z, and Z have beendetermined above, numerical trial values being substituted in equations(1) and (:2) until such values have been obtained for all of thepotentiometerequalizer resistances as will give, for the varioussettings of the potentiometer equalizer and for the various frequenciesto be transmitted, repeater gains approximately the theoreticallycorrect ones as closely as practicable. y

In the above calculations the impedances Z Z Z and Z,, have been usedwithout regard to the vector relation of their components, because onlyapproximate results were desired, and experience has shown thatsuflicient accuracy is obtained with this method.

While balanced potentiometer-s have been disclosed, appropriate for thebalanced amhfiers shown, it is clear that the invention is alsoapplicable to repeaters and potentiometers not of the balanced type. Thespecific values of frequencies mentioned herein to facilitate theexplanation of the principle of the invention, are, of course, merelyillustrativevalues, and the invention is not re stricted to use inconnection with frequencies of such values.

The invention claimed is:

1. An attenuating device and an input and an output lead therefor, saiddevice comprising a resonant circuit, a resistance, means for connectingan adjustable amount of said resistance between said circuit and saidinput lead, and means for so connecting said output lead to saidresistance that during normal operation of saiddevice said output leadis at a potential between the potentials of the pointsof connection ofsaid input lead and said circuit to said resistance.

2. A repeater for connection in a transmision hne, said repeatercomprising an.

electron discharge tube having an anode, an electron discharge tubehaving a control elecresonant loop, a resistance, means connecting saidresistance to said control electrode, and meansmovable relatively tosaid resistance for connecting an adjustable amount of said resistancein series between said anode and said loop, and for thereby causing saidcontrol electrode to be connected to said resistance at a point whichduring repeating is at a potential between the potentials of the pointsof connection of said anode and said loop to'said resistance.

3. A potentiometer and an output lead therefor, said potentiometercomprising a resistance element, a tuned loop circuit connected to oneend thereof, tap connections of different resistances leading from intson said element, and a contact adjusta le to engage the free ends ofsaid tap connections, and said output lead being connected to a point onsaid potentiometer electrically remote from said tuned loop circuit.

4. A wave transmission system comprising apotentiometer and a source forsupplying thereto currents of a relatively low frequency and arelatively high frequency, said potentiometer comprising a resistanceelement, an output lead connected to one end of said element, a loopcircuit connected to the other end of said element and tuned to afrequency substantially as high as said relatively high frequency, tapconnections of different resistances leading from different points onsaid element, and a contact adjustable to en gage the free ends of saidconnections, the resistances of and between said tap connections, theresistance, inductance, and capacity of said tuned loop circuit and theimpedance of said source being so proportioned that movement of saidadjustable contact from a tap connection of one resistance to a tapconnection of a higher resistance causes a ter decrease in transmissionat said relatively high frequency than at said relatively low frequency.

5. In a transmission line, a combined-potentiometer and attenuationequahzer comrising fixed reactive impedance and variable resistance inshunt to the line and variable resistance and substantially no'reactance in series with the line, and means for simultaneously sovarying .said shunt and seriesresistances as to compensate for unequalva-" riations in line attenuation at different frequencies.

In witness whereof, I hereunto subscribe my name this 16th day of June,A. D., 1922.

JACOB S. JR.

